fling mud
To disparage someone, especially to the detriment of their reputation. I'm trying to maintain a fair and respectable campaign, and my opponent has no problem flinging mud!
fling (or sling or throw) mud
make disparaging or scandalous remarks or accusations. informal The proverb throw dirt (or mud) enough, and some will stick , to which this phrase alludes, is attributed to the Florentine statesman Niccolò Machiavelli ( 1469–1527 ).
fling/sling/throw ˈmud (at somebody)
(informal) try to damage somebody’s reputation by telling other people bad things about them: Just before an election, politicians really start to sling mud at each other. ▶ ˈmud-slinging noun: There’s too much mud-slinging by irresponsible journalists.